Perpendicular recording has been developed in part to achieve higher recording density than is realized with longitudinal recording devices. A PMR write head typically has a main pole layer with a small surface area at an ABS, and coils that conduct a current and generate a magnetic flux in the main pole such that the magnetic flux exits through a write pole tip and enters a magnetic medium (disk) adjacent to the ABS. Magnetic flux is used to write a selected number of bits in the magnetic medium and typically returns to the main pole through two pathways including a trailing loop and a leading loop. The trailing loop has a trailing shield structure with first and second trailing shield sides at the ABS. The second (PP3) trailing shield arches over the write coils and connects to a top yoke that adjoins a top surface of the main pole layer near a back gap connection. The leading loop includes a leading shield with a side at the ABS and that is connected to a return path (RTP) proximate to the ABS. The RTP extends to the back gap connection (BGC) and enables magnetic flux in the leading loop pathway to return from the leading shield at the ABS and through the BGC to the main pole layer. A PMR head which combines the features of a single pole writer and a double layered medium (magnetic disk) has a great advantage over LMR in providing higher write field, better read back signal, and potentially much higher areal density.
The double write shield (DWS) design that features the leading and trailing loops was invented for ATE improvement by reducing stray field in side shields and in the leading shield. Magnetic flux is able to flow evenly through the leading loop and trailing loop. Compared with a non-DWS configuration where there is only a closed loop from the trailing side of the main pole, a DWS structure has better ATE. However, since flux in the trailing loop of a DWS configuration is only 50% of that in a non-DWS design, the result is a degraded hot seed (HS) response and therefore a loss in ADC. The hot seed is a magnetic layer with high saturation magnetization from 19 to 24 kG formed between a top surface of the write gap and a bottom surface of the first trailing shield at the ABS. A good HS response is required to reduce stray fields in the side shields and leading shield. In particular, it is desirable to have the potential of the HS more negative compared with the main pole potential.
Perpendicular magnetic recording has become the mainstream technology for disk drive applications beyond 150 Gbit/in2. As the demand for hard disk drives (HDD) based on PMR head technology has increased, stray field robustness becomes more and more important in order to minimize on-track bit error rate (BER) and servo erasure when a stray field is applied. With the growing demand for cloud storage and cloud-based network computing, high and ultra high data rate recording becomes important for high-end disk drive applications. Thus, it is essential to design a PMR writer that can achieve high area density capability (ADC) in addition to improved stray field robustness characterized by low ATE and a BER of about 10−6.